Method and apparatus for interchanging data between two devices in an automation network

ABSTRACT

A method for interchanging data between two devices in a network which utilizes a communication protocol with an interface based on an Object Linking and Embedding for Process Control Unified Architecture (OPC-UA) standard to interchange the data, wherein the communication protocol includes a priority allocation function which can allocate to the data at least two different priority values, and the data are interchanged based on the allocated priority values, such that the data interchangeable between the two devices in a predetermined period of time with a prescribed probability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/EP2011/056562 filed26 Apr. 2011. Priority is claimed on German Application No. 10 2010 021450.7 filed 25 May 2010, the content of which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for interchanging data between twodevices in a network, where the method uses a communication protocolhaving an interface conforming to the OPC-UA standard for the purpose ofinterchanging the data. The invention also relates to an apparatus forinterchanging data between two devices as well as to a network having atleast two devices and such an apparatus.

2. Description of the Related Art

Crevatin, M. et al., “Security for Industrial Communication Systems”,Proceedings of the IEEE, Vol. 93, No. 6, Jun. 1, 2005, pages 1152-1177(“Crevatin”), describes a method for exchanging data between two devicesin a network, where the method communication protocol having aninterface conforming to the OPC standard for the purpose ofinterchanging the data. In dependently thereof, Crevatin mentions theuse of IEEE 802.IQ VLAN and priority schemes to enable fast transmissionof data with a very low time delay for time-critical applications bybypassing IP layers.

WO 2007/105979 A1 cites, in connection with a synchronization of asoftware agent with a system cycle in an automation system, an OPC-UA(United Architecture) interface to allow web-based access to parts of anautomation system.

FIG. 1 shows a schematic representation of an automation network. Aplurality of devices 8 that receive data from sensors 10 and outputsuitable control data to actuators 9 are located on what is termed thefield level of an industrial automation system. Within this scheme thedevices 8 can be in operative contact with the sensors 10 and actuators9 as autonomous computers, or the devices 8 can be embedded systems. Inparticular, the devices 8 can possess their own individual controlfirmware. Additionally shown by way of example is a computer 7 that ispresent at the control level (PLC). The computer 7 and the devices 8 areused for open- or closed-loop control of associated machines of aninstallation. Within the automation network they reside on thesubnetworks of the networks referred to as the field network 4 or plantfloor network 3.

A link is formed between the plant floor network 3 and an automationnetwork 2 by way of a computer 6 having a supervisory control and dataacquisition (SCADA) system. The computer 6 is thus part of the processcontrol level by which technical processes in the plant floor network 3and field network 4 are monitored and controlled.

A computer 5 can be provided at a higher hierarchical level of theautomation network as part of an enterprise network 1. The computer 5can contain a manufacturing execution system (MES) and thus be part ofthe plant control level. Alternatively, the computer 5 can be equippedwith an enterprise resource planning (ERP) system as part of theenterprise level, where the ERP system deployed at the office levelconstitutes a complex software suite for supporting the resourceplanning of an enterprise (e.g., an SAP system).

It is usual practice to deploy non-realtime-capable star systems fornetwork communication at the office level. The Object Linking andEmbedding for Process Control (OPC) Unified Architecture (OPC-UA) systemaccording to the specifications of the OPC Foundation has establisheditself here as the new standard in network communications between theSCADA system of the computer 6 and the ERP system of the computer 5. Indata communication according to OPC-UA, data (values) is assigned aquality that also includes the rate at which the value is to be updated.Only such data is transmitted that has changed and whose attributesinitiate the necessity for the respective value to be transmitted.Accordingly, OPC-UA provides event-based communication. In this regard,OPC-UA is based on a remote procedure call (RPC) mechanism, as is knownfor example in standard Ethernet, TCP/IP (Transmission ControlProtocol/Internet Protocol) or also http-based networks. According tothe RPC mechanism, a request by a client on a server leads to aprocedure being called on the server for the purpose of processing therequest. Only when the processing of the request has been completed anda response has been sent from the server to the client, can the servercontinue the process that was interrupted by the request. This is theclassic communications architecture of inter-process communication (IPC)in distributed systems. Concurrently running processes are causallydependent on one another.

OPC-UA, in contrast, knows the mechanism of what are referred to assubscriptions. In this scheme, a receiver takes out a subscription toreceive a specific selection of information or data from a sender. Ifthe set of information or selection of data is subsequently changed, thesender will independently send the changes to the receiver. Thismechanism can be parameterized, because it can be specified, forexample, at what time interval at the earliest changes are to be sent.

With OPC-UA, the industry has available to it a standard protocol withthe aid of which it is possible, on the one hand, to model the mostdisparate forms of information (alarms or process values) in aninformation model and, on the other hand also, to transport theinformation. For this purpose there are service sets and services, asthey are called, which make the corresponding functionalities available.With OPC-UA, it is possible for the first time to utilize thisconvenient form of information transmission in the embedded sector also.This makes OPC-UA a powerful tool in the information modeling field.

Whereas OPC-UA is currently used mainly in the automation network 2, forexample, in SCADA systems, other requirements entirely are expected tobe fulfilled by the communication protocols in the plant floor network 3and/or field network 4. In the automation environment, it is necessaryto synchronize a plurality of devices 8 via communication links. Therequirements to be met by the synchronization are very diverse. Theyextend as far as hard realtime requirements, for example, with respectto the synchronization of drive shafts in a paper mill. In particular onthe plant floor, where the field level meets the office level, EthernetTCP/IP-based infrastructures are often already in use, for example, forcommunication between head controllers and/or SCADA/MES systems.

In these cases, it is usual to employ what are known as clockedprotocols. This means that the time is subdivided into time slices andit is planned precisely in advance which device may send, how and howmuch, within one timing cycle. Cyclic process maps (tables containinginput-output values) are exchanged between the communication partners.The following rule applies here: The shorter the cycle (higher clockrate), the better is the synchronization capability and the more datamust be continuously transmitted. A doubling of the clock rate leads tothe doubling of the overall communication volume. All the data is alwayssent in each cycle, irrespective of whether the same time requirementsapply to all the values or whether values have changed. Thiscommunication principle is usual on the field level in automationtechnology to ensure that the hard realtime requirements that prevailthere can be fulfilled.

In the decentralized peripherals environment, realtime communication canin this case occur, for example, by way of the Profinet IO communicationprotocol. This enables data interchange between Ethernet-based fielddevices 8. A further Ethernet-based approach for automation technologyis Industrial Real Time Ethernet (IRTE). According to IRTE,communication on the network is preplanned completely to rule outunwanted data collisions. However, this model is very static, because itis unable to respond to changes without new planning. The planning ishighly complex and can only be accomplished with the aid of a tool,because time responses due, for example, to cable lengths must also betaken into account. IRTE is primarily used for planning line structures.The advantage consists in strict determinism being established.

As a result, the office and/or control level and the field level areseparated in terms of the communication protocols used in theirsubnetworks. The communication protocols used in each case satisfydifferent requirements. In certain situations, the realtime requirementsprevailing on the field level may be irrelevant to the office level. Theexpression “vertical integration of automation technology” is understoodto mean the aspiration to integrate the different subnetworks and createa standardized communications structure from the enterprise level rightdown to the field level.

Hard realtime requirements exist in many fields of application ofautomation technology, for example, when shafts are to be synchronizedwith a high degree of precision. In hard realtime scenarios, data mustbe interchanged between two devices within a predefined time period.Communication occurs strictly deterministically. If data is interchangedoutside of a specified time interval, the data no longer fulfills therealtime requirements. What is to be understood to mean by realtime isdefined in particular in DIN 44300.

In the case of soft realtime requirements, the conditions imposed on thetemporal progression of the data interchange are less stringent. It issimply necessary to ensure that the data interchange between two devicesis completed within a predetermined time period with a predefinedprobability. For example, it can be provided that, with regard to adistribution of the time instants at which the data interchange occurs,the average value of the distribution always lies within a predefinedtime interval. Soft realtime requirements are sufficient in many fieldsof application of automation technology. This is the case primarilywhen, owing to the nature of the automation task in hand, therequirements are not so time-critical.

Accordingly, approaches exist for communication protocols that fulfillsoft realtime requirements, such as Soft Real Time (SRT) Ethernet. Inthe case of SRT, Ethernet priority mechanisms are used to makeconventional Ethernet and/or TCP/IP communication soft-realtime-capableand thus enable the communication to occur in addition to theconventional data traffic. In the case of SRT, collisions between datapackets, although avoided, are not ruled out completely. It is notnecessary to preplan communications on the network completely. Forexample, the time response of the data packets must not necessarily beplanned, but only the paths for the prioritized communication. As isusual practice in the case of Ethernet or office communication, starstructures can be planned.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method, an apparatus and anetwork by which it is possible to achieve an improved integration ofsubnetworks.

This and other objects and advantages are achieved by providing amethod, an apparatus, and a network, where the method in accordance withthe invention is used for interchanging data between two devices of anetwork, and where the method utilities a communication protocol havingan interface conforming to the OPC-UA standard for the purpose ofinterchanging the data. In this case, the communication protocolincludes a priority allocation function by which at least two differentpriority values can be assigned to the data and the data interchangeoccurs as a function of the assigned priority values, such that the datacan be interchanged between the two devices within a predetermined timeperiod with a predefined probability.

OPC-UA (Object Linking and Embedding for Process Control UnifiedArchitecture) is an OPC specification of the OPC Foundation and isdescribed at on the Internet at a website maintained by thatorganization. The priority allocation function can be particularlyimplemented as a Soft Real Time extension in the communication protocol.In particular, it can be provided that the application protocol ofOPC-UA is not changed, while the protocol layer of OPC-UA is modified bythe Soft Real Time extensions. In particular, the priority allocationfunction can assign priority values to the data such that in the eventof a collision of data on the network, in a switch or router, forexample, it is specified by way of the priority values which data willbe forwarded preferentially. In an embodiment, specific high-priorityvalues are allocated to such data, the interchange of which is intendedto satisfy soft realtime requirements. Such data can then beinterchanged between two devices within a predetermined time period witha predefined probability. The priority allocation function can beembodied in particular in accordance with a Soft Real Time applicationknown from the prior art. In another embodiment, TCP/IP packets aremodified in accordance with suitable Soft Real Time extensions.

With the Soft Real Time approach, realtime requirements can be fulfilledwithin a certain framework without the need, for example, to marshal thecorresponding resources required for an IRTE solution. A conventionalOPC-UA communication protocol can be trained with only minor changes fordeployment in Soft Real Time environments virtually without restrictingthe conventional TCP/IP environment. Communication between a server inwhich the communication protocol in accordance with the method of theinvention is used and a server that uses the conventional OPC-UAcommunication protocol can occur via a simple multiprotocol router,without any necessity for special hardware.

The invention is based on the consideration of modifying OPC-UA by SoftReal Time extensions such that the OPC-UA communication, which is infact not realtime-capable, will henceforth have soft realtimecharacteristics. Through the combination of an OPC-UA interface and thepriority allocation function in a communication protocol, a form ofcommunication is made possible that satisfies soft realtime requirementsand meets many of the requirements in automation technology. The thusrealized communication protocol can be implemented in a simple anduncomplicated manner in field level devices. Furthermore, problem-freedata interchange with OPC-UA-based devices of higher levels, such as theautomation network or the enterprise network is ensured. A high degreeof compatibility between subnetworks of an automation plant is achievedand the vertical integration substantially improved. The communicationprotocol is characterized by a high degree of efficiency becausesuperfluous data interchange is reliably avoided, in particular owing tothe OPC-UA component. At the same time, the priority allocation functionassures the realtime functionality according to Soft Real Time.

Preferably, the priority allocation function assigns a first priorityvalue to a first type of data and a second priority value to a secondtype of data, where, for a predefinable network structure via which theinterchange of the data between the two devices is executed, it isensured based on the assigned priority values that in the event of acollision between the data of the first type and data of the secondtype, the data of the second type is transmitted preferentially. Bycollision is to be understood in particular the simultaneous arrival ofdata packets at a nodal point of the network, such as a switch orrouter. In a collision situation, it is in particular not specifieddeterministically which of the two data packets will be forwardedpreferentially by the switch. A collision situation can also be presentwhen a data packet is already being processed by the switch while asecond data packet arrives, with the result that the second data packetcannot be processed further immediately, but is interrupted in itsonward transport until such time as the first data packet has beencompletely processed. In such a collision situation, the priority valuesensure that the data of the second type is handled preferentially overthe data of the first type. It can also be provided in particular that aprocessing of the data of the first type that has already started willbe interrupted if data of the second type arrives, so that the data ofthe second type will now be processed preferentially and forwarded onthe network. In this way, determinism is reestablished at branch pointsof the network. In particular, the data of the second type can then besuch data that must satisfy soft realtime requirements. therealtime-relevant data is then forwarded with a higher priority thanother data for which compliance with a transmission time window is lesscritical.

Preferably, time windows for interchanging data of the second type arespecified such that, for a predefinable network structure, a collisionprobability of two data packets, each of which contains data of thesecond type exclusively, does not exceed a predefinable threshold valueprobability. It is particularly preferred in this case if the timewindows for interchanging the data of the second type are specified byparameterizing a periodic synchronization clock between the two devices.By preplanning a clock rate, it can be ensured that no two high-prioritydata packets containing data of the second type converge simultaneouslyat a switch. In this way, collision situations are reliably avoided.Realtime-capable data interchange is guaranteed.

Preferably, it can be provided that the network structure is embodiedsuch that a network-related collision probability of data packets, eachof which contains data of the second type exclusively, does not exceed apredefinable network-related threshold value probability. Preferably,the network structure will then be embodied in that communication linksand/or communication nodes are selected such that the network-relatedcollision probability does not exceed the network-related thresholdvalue probability. By intelligent forward planning, it is possible, forexample, to configure cable routes within the network and also thepositions of nodes (switches and/or routers) such that the probabilityof a collision of data of the second type is reduced to an absoluteminimum. Determinism is ensured to a certain degree as a result of thedefinition of threshold value probabilities. The risk that collisionswill occur can be kept within limits. This very effectively enablesfulfillment of the condition that the data must be interchanged betweenthe two devices within a predetermined time period with a predefinedprobability.

It is also an object of the invention to provide an apparatus that isused for interchanging data between two devices of a network, where theapparatus utilizes a communication protocol having an interfaceconforming to the OPC-UA standard for the purpose of interchanging thedata. In this case, the communication protocol has a priority allocationfunction by which at least two different priority values can be assignedto the data. The communication protocol guarantees that the datainterchange occurs as a function of the assigned priority values, withthe result that the data can be interchanged between the two deviceswithin a predetermined time period with a predefined probability.

A network in accordance with the invention comprises at least twodevices as well as an apparatus in accordance with the invention.

The preferred embodiments illustrated with reference to the method inaccordance with the inventions and their advantages apply analogously tothe apparatus and network.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims. It should be further understood that thedrawings are not necessarily drawn to scale and that, unless otherwiseindicated, they are merely intended to conceptually illustrate thestructures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with reference toexemplary embodiments taken in conjunction with the accompanyingfigures, in which:

FIG. 1 shows a schematic block diagram of a conventional multilayernetwork of an automation plant;

FIG. 2A shows a schematic block diagram of the data interchange betweentwo devices, where a collision situation occurs between sent datapackets in accordance with the invention;

FIG. 2B shows a schematic block diagram of the data interchange betweentwo devices, where a collision situation is avoided through allocationof suitable priority values in accordance with the invention;

FIG. 3A shows a schematic block diagram of a network infrastructureaccording to the prior art;

FIG. 3B shows a schematic block diagram network infrastructure inaccordance with the invention;

FIG. 4 shows a schematic block diagram of a device which, for thepurpose of interchanging data in a network, makes use of a communicationprotocol according to an exemplary embodiment of the invention method inaccordance with the invention; and

FIG. 5 is a flowchart of the method in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Identical or functionally identical elements are labeled with the samereference signs in the figures.

The invention permits OPC-UA to be used in the field of realtimecommunication (deterministic communication). OPC-UA, which waspreviously employed mainly in the automation network 2 (for example, inthe computer 6 containing the SCADA system), can now make inroads intothe plant floor network 3 and/or field network 4. Within the automationpyramid, the application range of OPC-UA is extended downward in thepyramid through use of the method in accordance with the invention.Efforts are being made to deploy OPC-UA further still up to the computer5 containing the ERP and/or MES system in the enterprise network 1.Consequently, what is achieved as a result is end-to-end communicationand a unified view onto the process data from the lowest level right upto the ERP level. The same technology is employed throughout, thusensuring complete interoperability without the necessity for additionalhardware (mappers or converters).

A strength of OPC-UA is its power in information modeling, which issimultaneously used to improve or enable the interoperability ofcomponents. All the devices 8 involved provide not only their processvalues, but in addition also semantic information concerning thesevalues in the information model. This advantage now extends itseffect—without additional overhead—right into the plant floor network 3.

FIG. 2A schematically illustrates the communication of a device 8 a witha device 8 c and the communication of the device 8 b with a device 8 c.For this purpose, the devices 8 a and 8 b send data packets D1 over datalines 22 to the device 8 c. In this scheme, the network 24 has a node inthe form of a switch 18, via which the data packets D1 must run to reachthe device 8 c. It is possible that the data packets D1 arrivesimultaneously at the switch 18, thus creating a collision situation.The switch 18 must decide which of the data packets D1 is to beforwarded first to the device 8 c.

With the conventional IRTE-based communication, determinism is no longergiven in the situation shown. If a collision occurs, it is no longerclear which of the data packets D1 is to be forwarded first. In order toprevent this situation, all traffic over the network 24 must bepreplanned completely. In the case of IRTE communication, the switch 18is in this instance embodied as a special IRTE switch havingIRTE-specific hardware.

In accordance with an exemplary embodiment of the method of theinvention, a priority allocation function provides Soft Real Timefunctionality. This means that suitable priority values are assigned todata packets D1 and D2. In the exemplary embodiment of FIG. 2B, the datain the data packet D2 is such data as is essential for thesynchronization of the devices 8 a and 8 c. The data must consequentlysatisfy realtime requirements. Determinism must be established withregard to its transmission on the data line 22. For this reason, thepriority allocation function of the communication protocol 11implemented in the device 8 a assigns a high-priority value to the datapacket D2.

The device 8 b, in contrast, only needs to transmit to the device 8 cdata that characterizes an operating condition of the device 8 b, forexample, its current temperature. The time at which the device 8 creceives this information is not especially relevant. For this reason;the priority allocation function provided in the communication protocol11 of the device 8 b assigns a low priority to the data packet D1.

If a collision now occurs between the data packets D1 and D2 containingthe priority information at the switch 18, which likewise supports thecommunication protocol 11 implemented in the devices 8 a and 8 b, thehigher-priority data packet D2 is preferentially forwarded to the device8 c. Determinism is hereby ensured with regard to the data packet D2 andrealtime-capable communication between the devices 8 a and 8 c isachieved.

By means of suitable forward planning, it is merely necessary to ensurethat a high-priority data packet D2 is not sent by the device 8 b to thedevice 8 c simultaneously with the sending of such a data packet by thedevice 8 a. In practice, this can be achieved statically, i.e.,time-independently, by planning communication paths. Practice shows thatin most cases the communication paths on which high-priority packets runcan be set up disjointly with respect to one another.

In particular, OPC-UA subscriptions can be marked as high-priority datapackets D2 by the priority allocation function. Accordingly, it becomespossible through the use of the Soft Real Time approach to send OPC-UAsubscriptions (more precisely, the change messages of a subscription)such that they precisely satisfy the Soft Real Time requirements.

This method improves interoperability on a network structure, as shownin FIG. 1. In accordance with the prior art, a blue box 21 was requiredin the past to serve as a communication bridge or intermediary betweenthe OPC-UA- or TCP/IP-based office network 19 and the field network 20based, for example, on Profinet IO. In the schematic representation inFIG. 3A, the bluebox 21 communicates in the direction of the fieldnetwork 20 by Profinet IO and accordingly is a subscriber in the fieldnetwork 20. In the direction of the office network 19, the bluebox 21 isable to communicate with an SAP system on the computer 5, for example,via Web Services or OPC-UA. In that case, it is a subscriber in theoffice network 19.

In the method in accordance with the invention having the OPC-UAcommunication protocol modified by the priority allocation function, thebluebox 21 can be omitted in the network 24, as shown in FIG. 3B. Usingthe Soft Real Time extension of OPC-UA, a compatible communicationsenvironment is created both in the office network 19 and in the fieldnetwork 20, thereby enabling the bluebox 21 to be dispensed with.Conventional TCP/IP communication and OPC-UA/SRT communication cancoexist without mutual interference.

FIG. 4 provides a further schematic illustration of a possible structureof the communication protocol 11 which is present in the device 8 a. Thedevice 8 a comprises a computer in which the communication protocol 11is installed in executable form. In this case, the communicationprotocol 11 comprises a plurality of layers with associated interfaces.Specifically, these are an application layer 12, a Unified Architecture(UA) stack 14 having an OPC-UA interface 13, a TCP/IP interface 15, anEthernet interface 16, and a physical interface 17. In addition, a SoftReal Time extension 23 is now provided that implements the priorityallocation function. Depending on the type of the data, this issupplemented by the Soft Real Time extension 23 with priorityinformation or a priority value. It is particularly preferred in thiscase if the communication protocol 11 is implemented as a multilayerstructure based on the Open Systems Interconnection reference model (OSIlayer model of the International Standards Organization).

Overall, the advantages provided by OPC-UA and SRT are optimallycombined within the communications on the network 24. The subscriptionsprinciple used in OPC-UA guarantees that all the relevant data istransmitted, while at the same time the volume of data is low. SRT, onthe other hand, guarantees realtime capability to a certain degree.Centralized preplanning of the communication is necessary to a lesserextent than according to the prior art. There is nonetheless an increasein the total volume of data that can be transmitted. Data fordeterministic and non-deterministic communication can be processed veryefficiently by the communication protocol. In addition a high level ofinteroperability on the network 24 is ensured.

FIG. 5 is a flow chart of a method for interchanging data between twodevices of a network, where the method utilizes a communication protocolhaving an interface conforming to an Object Linking and Embedding forProcess Control Unified Architecture (OPC-UA) standard to interchangethe data. The method comprises assigning at least two different priorityvalues to the data via a priority allocation function of thecommunication protocol, as indicated in step 510.

The data is then interchanged as a function of the assigned at least twodifferent priority values such that the data is interchangeable betweenthe two devices within a predetermined time period with a predefinedprobability, as indicated in step 520.

While there have been shown, described and pointed out fundamental novelfeatures of the invention as applied to a preferred embodiment thereof,it will be understood that various omissions and substitutions andchanges in the form and details of the methods described and the devicesillustrated, and in their operation, may be made by those skilled in theart without departing from the spirit of the invention. For example, itis expressly intended that all combinations of those elements and/ormethod steps which perform substantially the same function insubstantially the same way to achieve the same results are within thescope of the invention. Moreover, it should be recognized thatstructures and/or elements and/or method steps shown and/or described inconnection with any disclosed form or embodiment of the invention may beincorporated in any other disclosed or described or suggested form orembodiment as a general matter of design choice. It is the intention,therefore, to be limited only as indicated by the scope of the claimsappended hereto.

The invention claimed is:
 1. A method for interchanging data between twodevices of a network, said method utilizing a communication protocolhaving an interface conforming to an Object Linking and Embedding forProcess Control Unified Architecture (OPC-UA) standard to interchangethe data, the method comprising: assigning at least two differentpriority values to the data via a priority allocation function of thecommunication protocol; and interchanging the data in accordance withthe OPC-UA standard as a function of the assigned at least two differentpriority values such that the data is interchangeable in accordance withthe OPC-UA standard between the two devices within a predetermined timeperiod with a predefined probability; wherein the priority allocationfunction assigns a first priority value to a first type of data and asecond priority value to a second type of data; and wherein, for apredefinable network structure via which the interchange of the data inaccordance with the OPC-UA standard between the two devices executes,the data of the second type is transmitted based on the assignedpriority values in an event of a collision between the first type ofdata and the second type of data.
 2. The method as claimed in claim 1,wherein time windows for interchanging data of the second type inaccordance with the OPC-UA standard are specified such that, for apredefinable network structure, a probability of collision of two datapackets, each of which exclusively contains the second type of data,does not exceed a predefinable threshold value probability.
 3. Themethod as claimed in claim 2, wherein the time windows for interchangingthe second type of data in accordance with the OPC-UA standard arespecified by parameterization of a periodic synchronization clockbetween the two devices.
 4. The method as claimed in claim 1, wherein astructure of the network is configured such that a network-relatedcollision probability of two data packets, each of which contains dataof the second type exclusively, does not exceed a predefinablenetwork-related threshold value probability.
 5. The method as claimed inclaim 4, wherein the structure of the network is configured such that atleast one of communication links and communication nodes are selectedsuch that the network-related collision probability does not exceed thepredefinable network-related threshold value probability.
 6. Anapparatus for interchanging data between two devices of a network, saidapparatus utilizing a communication protocol having an interfaceconforming to an Object Linking and Embedding for Process ControlUnified Architecture (OPC-UA) standard to interchange the data; whereinthe communication protocol includes a priority allocation function bywhich at least two different priority values are assignable to the data;wherein the communication protocol ensures that the interchange of thedata occurs in accordance with the OPC-UA standard as a function ofassigned priority values such that the data is interchanged inaccordance with the OPC-UA standard between the two devices within apredetermined time period with a predefined probability; wherein thepriority allocation function assigns a first priority value to a firsttype of data and a second priority value to a second type of data; andwherein, for a predefinable network structure via which the interchangeof the data in accordance with the OPC-UA standard between the twodevices executes, the data of the second type is transmitted based onthe assigned priority values in an event of a collision between thefirst type of data and the second type of data.
 7. A network comprisingat least two devices having the apparatus as claimed in claim 6.